Multichromophoric forster resonance energy transfer from B800 to B850 in the light harvesting complex 2: Evidence for subtle energetic optimization by purple bacteria
Multichromophoric forster resonance energy transfer from B800 to B850 in the light harvesting complex 2: Evidence for subtle energetic optimization by purple bacteria
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DOI：
10.1021/jp070111l
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发表时间：
2007-06-21
影响因子：
3.3
通讯作者：
Silbey, Robert J.
中科院分区：
文献类型：
--
作者：
Jang, Seogjoo;Newton, Marshall D.;Silbey, Robert J.
这项工作提供了我们的多色Forster共振能量转移(MC-FRET)理论(物理)的应用的详细说明。莱特牧师。2004，92,218301)，用于计算紫色细菌的捕光复合体2(LH2)中从B800单元到B850单元的能量转移率。模型哈密顿量由单个细菌-叶绿素(BCHL)代表的B800单元、由其整个BChl集合代表的B850单元、两个单元之间的电子耦合以及代表所有环境自由度的BASH项组成。模型参数独立于速率计算，从文献数据并通过对系综线形状的拟合来确定。假设介质的光介电常数在1.5-2范围内，比较我们的理论速率和低温实验速率，我们估计BCHL-Q(Y)跃迁偶极子的大小在6.5-7.5D之间。我们研究了B800-BCHL的平均激发能量相对于B850-BCHL的平均激发能量的偏差是如何影响能量转移时间的，方法是基于我们的MC-FRET理论和原始的FRET理论计算转移速率，改变偏移值。在我们的模型中，我们发现从拟合到系综线形确定的偏差260 cm(-1)的值非常接近MC-FRET和FRET速率之比达到最大值时的值。这为细菌系统以建设性的方式利用B850中多个生色团之间的量子力学相干，从而实现从B800到B850的高效能量转移提供了证据。
This work provides a detailed account of the application of our multichromophoric Forster resonance energy transfer (MC-FRET) theory (Phys. Rev. Lett. 2004, 92, 218301) for the calculation of the energy transfer rate from the B800 unit to the B850 unit in the light harvesting complex 2 (LH2) of purple bacteria. The model Hamiltonian consists of the B800 unit represented by a single bacteriochlorophyll (BChl), the B850 unit represented by its entire set of BChls, the electronic coupling between the two units, and the bath terms representing all environmental degrees of freedom. The model parameters are determined, independent of the rate calculation, from the literature data and by a fitting to an ensemble line shape. Comparing our theoretical rate and a low-temperature experimental rate, we estimate the magnitude of the BChl-Q(y) transition dipole to be in the range of 6.5-7.5 D, assuming that the optical dielectric constant of the medium is in the range of 1.5-2. We examine how the bias of the average excitation energy of the B800-BChl relative to that of the B850-BChl affects the energy transfer time by calculating the transfer rates based on both our MC-FRET theory and the original FRET theory, varying the value of the bias. Within our model, we find that the value of bias 260 cm(-1), which we determine from the fitting to an ensemble line shape, is very close to the value at which the ratio between MC-FRET and FRET rates is a maximum. This provides evidence that the bacterial system utilizes the quantum mechanical coherence among the multiple chromophores within the B850 in a constructive way so as to achieve efficient energy transfer from B800 to B850.